Effects of salinity, DOM and metals on the fate and microbial toxicology of propetamphos formulations in river and estuarine sediment

Toxicity studies tend to use pure pesticides with single organisms. However, natural systems are complex and biological communities diverse. The organophosphate pesticide propetamphos (PPT) has been found exceeding regulatory limits (100 ng L⁻¹) in rivers. We address whether solution properties affect the fate of Analar (Analar-PPT) or industrial PPT (PPT-Ind) propetamphos formulations and whether propetamphos and metal toxicant effects are additive, antagonistic or synergistic? The sorption, desorption, biodegradation and microbial toxicology of Analar-PPT and PPT-Ind were investigated in Conwy River and estuary sediment. Results showed elevated salinity enhanced PPT sorption, while higher salinities increased PPT-Ind retention. Higher dissolved organic matter (DOM) and low salinity slowed Analar-PPT biodegradation (1.9 × 10⁻³ h⁻¹). Analar-PPT and PPT-Ind biodegradation was further reduced by low salinity, high DOM and dissolved Zn and Pb (6.3 × 10⁻⁴ h⁻¹, 1100 h t_½ for Analar-PPT; 7.5 × 10⁻⁴ h⁻¹, 924 h t_½ for PPT-Ind). Toxicity effects of PPT, Zn and Pb in equitoxic ratio were higher for PPT-Ind (4.7 μg PPT-Ind g⁻¹; 581 μg Zn g⁻¹; 395 μg Pb g⁻¹) than for Analar-PPT (34.6 μg PPT g⁻¹; 312 μg Zn g⁻¹; 212 μg Pb g⁻¹) whilst a toxicant ratio 1:100:10 suggested small quantities of Analar-PPT (EC₁₀ = 0.06 μg g⁻¹) affected microbial communities. The combined toxicity effect was more than additive. Thus, industrial formulations and pollutant mixtures should be considered when assessing environmental toxicity.     

Nitrate-induced photodegradation of atenolol in aqueous solution: kinetics, toxicity and degradation pathways

The extensive utilization of β-blockers worldwide led to frequent detection in natural water. In this study the photolysis behavior of atenolol (ATL) and toxicity of its photodegradation products were investigated in the presence of nitrate ions. The results showed that ATL photodegradation followed pseudo-first-order kinetics upon simulated solar irradiation. The photodegradation was found to be dependent on nitrate concentration and increasing the nitrate from 0.5 mM L⁻¹ to 10 mM L⁻¹ led to the enhancement of rate constant from 0.00101 min⁻¹ to 0.00716 min⁻¹. Hydroxyl radical was determined to play a key role in the photolysis process by using isopropanol as molecular probe. Increasing the solution pH from 4.8 to 10.4, the photodegradation rate slightly decreased from 0.00246 min⁻¹ to 0.00195 min⁻¹, probably due to pH-dependent effect of nitrate-induced OH formation. Bicarbonate decreased the photodegradation of ATL in the presence of nitrate ions mainly through pH effect, while humic substance inhibited the photodegradation via both attenuating light and competing radicals. Upon irradiation for 240 min, only 10% reduction of total organic carbon (TOC) can be achieved in spite of 72% transformation rate of ATL, implying a majority of ATL transformed into intermediate products rather than complete mineralization. The main photoproducts of ATL were identified by using solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) techniques and possible nitrate-induced photodegradation pathways were proposed. The toxicity of the phototransformation products was evaluated using aquatic species Daphnia magna, and the results revealed that photodegradation was an effective mechanism for ATL toxicity reduction in natural waters.     

Bioaccumulation and depuration of anthracene in Penaeus monodon (Fibricius) through food ingestion

Understanding on the bioaccumulation and depuration of PAHs (polycyclic aromatic hydrocarbons) in Penaeus monodon is important in seafood safety because it is one of the most popular seafood consumed worldwide. In this study, we used anthracene as the precursor compound for PAHs accumulation and depuration in the shrimp. Commercial feed pellets spiked with anthracene were fed to P. monodon. At 20 mg kg⁻¹ anthracene, P. monodon accumulated 0.1% of the anthracene from the feed. P. monodon deputed the PAH two times faster than its accumulation. The shrimp reduced its feed consumption when anthracene content in the feed exceeded 20 mg kg⁻¹. At 100 mg kg⁻¹ anthracene, P. monodon started to have necrosis tissues on the posterior end of their thorax. The bioaccumulation factor (BAF), uptake rate constant (k₁) and depuration rate constant (k₂) of anthracene in P. monodon were 1.15 × 10⁻³, 6.80 × 10⁻⁴ d⁻¹ and 6.28 × 10⁻¹ d⁻¹, respectively. The depuration rate constant is about thousand times higher than the uptake rate constant and this indicated that this crustacean is efficient in depurating hydrocarbons from their tissue.     

Hydrocarbon-utilizing microorganisms naturally associated with sawdust

Sawdust, one of the materials used as sorbent for removing spilled oil from polluted environments was naturally colonized by hydrocarbon-utilizing fungi, 1 × 10⁵-2 × 10⁵ colony forming units (CFU) g⁻¹, depending on the hydrocarbon substrate. This sorbent was initially free of hydrocarbon-utilizing bacteria. Incubating wet sawdust at 30 °C resulted in gradually increasing the fungal counts to reach after 6 months between 5 × 10⁶ and 7 × 10⁶ CFU g⁻¹, and the appearance of hydrocarbon-utilizing bacteria in numbers between 8 × 10⁴ and 3 × 10⁵ cells g⁻¹. The fungi belonged to the genera Candida (32% of the total), Penicillium (21%), Aspergillus (15%), Rhizopus (12%), Cladosporium (9%), Mucor (7%) and Fusarium (4%). Based on their 16S rRNA gene sequences the bacteria were affiliated to Actinobacterium sp. (38%), Micrococcus luteus (30%), Rhodococcus erythropolis, (19%) and Rhodococcus opacus (13%). Individual pure fungal and bacterial isolates grew on a wide range of individual pure aliphatic (n-alkanes with chain lengths between C₉ and C₄₀) and aromatic (benzene, biphenyl, anthracene, naphthalene and phenanthrene) hydrocarbons as sole sources of carbon and energy. Quantitative determinations revealed that all fungal and bacterial isolates could consume considerable proportions of crude oil, phenanthrene (an aromatic hydrocarbon) and n-hexadecane (an aliphatic hydrocarbon) in batch cultures. It was concluded that when sawdust is used as a sorbent, the associated microorganisms probably contribute to the bioremediation of oil and hydrocarbon pollutants in the environment.     

SMX degradation by ozonation and UV radiation: a kinetic study

The rate constants of sulfamethoxazole (SMX) degradation by ozonation and UV₂₅₄ radiation were investigated under various parameters including influent ozone gas concentration, initial SMX concentration, UV light intensity, ionic strength, water quality in terms of varying anions (bicarbonate, sulfate and nitrate), humic acid (HA) and pH. The results indicated that the removal of SMX by ozonation and UV₂₅₄ radiation fitted well to a pseudo first-order kinetic model and the rate constants were in the range of (0.9-9.8) × 10⁻³ and (1.7-18.9) × 10⁻³ s⁻¹, respectively. The second-order rate constants of SMX with ozone (k_O3), under varying operational parameters, were also determined and varied in the range of (0.60-3.38) ± 0.13 × 10⁵ M⁻¹ s⁻¹. In addition, SMX degradation through UV pretreatment followed by ozonation in the presence of HA was proved to be an effective method which can remove SMX with a low ozone dose. The results suggested that ozonation of SMX was more affected by concentration of influent ozone gas, alkalinity, and HA, while incident UV light intensity, pH, and HA were the dominant factors influencing UV degradation of SMX.     

Adsorptive removal of an acid dye by lignocellulosic waste biomass activated carbon: equilibrium and kinetic studies

Chemically prepared activated carbon material derived from palm flower was used as adsorbent for removal of Amido Black dye in aqueous solution. Batch adsorption studies were performed for the removal of Amido Black 10B (AB10B), a di-azo acid dye from aqueous solutions by varying the parameters like initial solution pH, adsorbent dosage, initial dye concentration and temperature with three different particle sizes such as 100 μm, 600 μm and 1000 μm. The zero point charge was pH 2.5 and the maximum adsorption occurred at the pH 2.3. Experimental data were analyzed by model equations such as Langmuir, Freundlich and Temkin isotherms and it was found that the Freundlich isotherm model best fitted the adsorption data and the Freundlich constants varied from (K_F) 1.214, 1.077 and 0.884 for the three mesh sizes. Thermodynamic parameters such as ΔG, ΔH and ΔS were also calculated for the adsorption processes and found that the adsorption process is feasible and it was the endothermic reaction. Adsorption kinetics was determined using pseudo first-order, pseudo second-order rate equations and also Elovich model and intraparticle diffusion models. The results clearly showed that the adsorption of AB10B onto lignocellulosic waste biomass from palm flower (LCBPF) followed pseudo second-order model, and the pseudo second-order rate constants varied from 0.059 to 0.006 (g mg⁻¹ min) by varying initial adsorbate concentration from 25 mg L⁻¹ to 100 mg L⁻¹. Analysis of the adsorption data confirmed that the adsorption process not only followed intraparticle diffusion but also by the film diffusion mechanism.     

The association between total urinary arsenic concentration and renal dysfunction in a community-based population from central Taiwan

Arsenic (As) is an important environmental toxicant that can cause cancer and cardiovascular disease, but the relationship between As exposure and renal dysfunction is not clear. The aim of this study is to examine the association between As exposure and renal dysfunction in a community-based population in central Taiwan. One thousand and forty-three subjects were recruited between 2002 and 2005. The risk for type 2 diabetes was increased by 2-fold (p < 0.05) in subjects with total urinary As (U-As) > 75 μg g⁻¹ creatinine as compared with subjects whose U-As was ?35 μg g⁻¹ creatinine after the adjustment for potential confounders. The adjusted odds ratio for an abnormal β2 microglobulin (B2MG > 0.154 mg L⁻¹) was significantly higher in subjects with U-As > 35 μg g⁻¹ creatinine as compared with the reference group adjusted for age, sex, living area, cigarette smoking, diabetes, and hypertension. The risk for abnormal B2MG and estimated glomerular filtration rate (eGFR < 90 mL min⁻¹ (1.73 m²)⁻¹) was both increased around 2-fold (p < 0.05) in subjects with U-As > 75 μg g⁻¹ creatinine as compared with those with U-As ? 35 μg g⁻¹ creatinine adjusted for all the risk factors plus lead (Pb), cadmium and nickel. The prevalence of abnormal B2MG was 4.82 times higher in subjects with both over the median levels of U-As (85.1 μg L⁻¹) and urinary Pb (18.9 μg L⁻¹) as compared to both lower than the median (p < 0.001). These results indicate that U-As might relate to renal dysfunction even other important risk factors were taken into account. Follow-up studies for causal inference are warranted.     

Evaluation of food chain transfer of the antibiotic oxytetracycline and human risk assessment

There has been recent concern regarding the possibility of antibiotics entering the aquatic food chain and impacting human consumers. This work reports experimental results of the bioconcentration of the antibiotic oxytetracycline (OTC) by the Asian watermeal plant (Wolffia globosa Hartog & Plas) and bioaccumulation of OTC in watermeal and water by the seven-striped carp (Probarbus jullieni). They show, for the first time, the extent to which OTC is able to transfer from water to plant to fish and enter the food chain. The mean bioconcentration factor (dry weight basis) with watermeal was 1.28 × 10³ L kg⁻¹. Separate experiments were undertaken to characterize accumulation of OTC by carp from water and watermeal. These showed the latter pathway to be dominant under the conditions employed. The bioconcentration and biomagnification factors for these processes were 1.75 L kg⁻¹ and 2 × 10⁻⁴ kg g⁻¹ respectively. Using an aqueous concentration range of 0.34–3.0 μg L⁻¹, hazard quotients for human consumption of contaminated fish of 1.3 × 10⁻² to 1.15 × 10⁻¹ were derived.     

Salting-out phenomenon and 1-octanol/water partition coefficient of metalaxyl pesticide

In this paper, we present the effect of inorganic cations such as Na⁺, K⁺, Ca²⁺, Mg²⁺ on the salting-out phenomenon of metalaxyl from pure water to aqueous salt solutions. Moreover the 1-octanol/water partition coefficient in pure water is presented. To accomplish this, aqueous solubility of metalaxyl was determined in pure water, in different salt solution (NaCl, KCl, CaCl₂ and MgCl₂), and at different concentration level ranging from 0.01 to 1.5 M. The 1-octanol/water partition coefficient was determined using the static shake-flask method. Solubility was determined using dynamic saturation method for pure water in the range of 298.15-325.15 K and at 298.15 K for different salt solutions. The solubility value in pure water for studied interval was found constant (m = 3.118 × 10⁻² mol kg⁻¹).Solubility values were used to calculate the standard molar Gibbs free energy of dissolution (Δ_solG°) and transfer (Δ_trG°) at 298.15 K. The values of Δ_trG° from pure to all studied aqueous salt solutions did not exceed 2 kJ mol⁻¹, the value of Δ_solG° of dissolution is 18.5 ±0.72 kJ mol⁻¹. The 1-octanol/water partition coefficient in pure water log K_o/w is equal to 1.69. The obtained results confirm the classification of the neutral metalaxyl as a slightly hydrophobic molecule.     

Methyl-triclosan binding to human serum albumin: Multi-spectroscopic study and visualized molecular simulation

Methyl-triclosan (MTCS), a transformation product and metabolite of triclosan, has been widely spread in environment through the daily use of triclosan which is a commonly used anti-bacterial and anti-fungal substance in consumer products. Once entering human body, MTCS could affect the conformation of human serum albumin (HSA) by forming MTCS–HSA complex and alter function of protein and endocrine in human body. To evaluate the potential toxicity of MTCS, the binding mechanism of HSA with MTCS was investigated by UV–vis absorption, circular dichroism and Fourier transform infrared spectroscopy. Binding constants, thermodynamic parameters, the binding forces and the specific binding site were studied in detail. Binding constant at room tempreture (T = 298 K) is 6.32 × 10³ L mol⁻¹; ΔH⁰, ΔS⁰ and ΔG⁰ were 22.48 kJ mol⁻¹, 148.16 J mol⁻¹ K⁻¹ and −21.68 kJ mol⁻¹, respectively. The results showed that the interactions between MTCS and HSA are mainly hydrophobic forces. The effects of MTCS on HSA conformation were also discussed. The binding distance (r = 1.2 nm) for MTCS–HSA system was calculated by the efficiency of fluorescence resonance energy transfer. The visualized binding details were also exhibited by molecular modeling method and the results could agree well with that from the experimental study.     

Using native epiphytic ferns to estimate the atmospheric mercury levels in a small-scale gold mining area of West Java, Indonesia

Mercury pollution is caused by artisanal and small-scale gold mining (ASGM) operations along the Cikaniki River (West Java, Indonesia). The atmosphere is one of the primary media through which mercury can disperse. In this study, atmospheric mercury levels are estimated using the native epiphytic fern Asplenium nidus complex (A. nidus) as a biomonitor; these estimates shed light on the atmospheric dispersion of mercury released during mining.Samples were collected from 8 sites along the Cikaniki Basin during September-November, 2008 and September-November, 2009.The A. nidus fronds that were attached to tree trunks 1-3 m above the ground were collected and measured for total mercury concentration using cold vapor atomic absorption spectrometry (CVAAS) after acid-digestion. The atmospheric mercury was collected using porous gold collectors, and the concentrations were determined using double-amalgam CVAAS.The highest atmospheric mercury concentration, 1.8 × 10³ ± 1.6 × 10³ ng m⁻³, was observed at the mining hot spot, and the lowest concentration of mercury, 5.6 ± 2.0 ng m⁻³, was observed at the remote site from the Cikaniki River in 2009. The mercury concentrations in A. nidus were higher at the mining village (5.4 × 10³ ± 1.6 × 10³ ng g⁻¹) than at the remote site (70 ± 30 ng g⁻¹). The distribution of mercury in A. nidus was similar to that in the atmosphere; a significant correlation was observed between the mercury concentrations in the air and in A. nidus (r = 0.895, P < 0.001, n = 14). The mercury levels in the atmosphere can be estimated from the mercury concentration in A. nidus using a regression equation: log (Hg_A.nidu/ng g⁻¹) = 0.740 log (Hg_Air/ng m⁻³) − 1.324.     

Aerobic degradation of tetrabromobisphenol-A by microbes in river sediment

This study investigated the aerobic degradation of tetrabromobisphenol-A (TBBPA) and changes in the microbial community in river sediment from southern Taiwan. Aerobic degradation rate constants (k₁) and half-lives (t_1/2) for TBBPA (50 μg g⁻¹) ranged from 0.053 to 0.077 d⁻¹ and 9.0 to 13.1 d, respectively. The degradation of TBBPA (50 μg g⁻¹) was enhanced by adding yeast extract (5 mg L⁻¹), sodium chloride (10 ppt), cellulose (0.96 mg L⁻¹), humic acid (0.5 g L⁻¹), brij 30 (55 μM), brij 35 (91 μM), rhamnolipid (130 mg L⁻¹), or surfactin (43 mg L⁻¹), with rhamnolipid yielding a higher TBBPA degradation than the other additives. For different toxic chemicals in the sediment, the results showed the high-to-low order of degradation rates were bisphenol-A (BPA) (50 μg g⁻¹) > nonylphenol (NP) (50 μg g⁻¹) > 4,4′-dibrominated diphenyl ether (BDE-15) (50 μg g⁻¹) > TBBPA (50 μg g⁻¹) > 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether (BDE-209) (50 μg g⁻¹). The addition of various treatments changed the microbial community in river sediments. The results also showed that Bacillus pumilus and Rhodococcus ruber were the dominant bacteria in the process of TBBPA degradation in the river sediments.     

Dissolution of mimetite Pb5(AsO4)3Cl in low-molecular-weight organic acids and EDTA

Due to its relatively low solubility, mimetite Pb₅(AsO₄)₃Cl may control Pb and As(V) solution levels at a low value in contaminated soils. The time-dependent dissolution of mimetite by low-molecular-weight organic acids (LMWOAs) such as acetic, lactic, citric, and ethylene diamine tetra-acetic acid (EDTA) was determined. At pH 3.5, the presence of citric acid or EDTA significantly increases the solubility of mimetite while acetic or lactic acids show little effect. The effect of all organic anions on the dissolution of mimetite increased with the increase in solution pH. The rate of mimetite dissolution depended on the kind and concentration of organic solvents in the sequence r_EDTA > r_lactate > r_acetate > r_citrate. Soluble Pb and As(V) released in LMWOAs and EDTA were higher than the WHO guideline value for these elements in drinking water (10 μg As(V) L⁻¹, 10 μg Pb L⁻¹). This suggests that soil organic acids in rhizosphere can potentially liberate Pb and As(V) from mimetite in contaminated soils.     

Photocatalytic removal of organic pollutants in aqueous solution by Bi(4)Nb(x)Ta((1-x))O(8)I

In this work, Bi₄Nb_xTa_(1−x)O₈I photocatalysts have been synthesized by solid state reaction method and characterized by powder X-ray diffraction, scanning electron microscope and UV-Vis near infrared diffuse reflectance spectroscopy. The photocatalytic activity of these photocatalysts was evaluated by the degradation of methyl orange (MO) in aqueous solutions under visible light, UV light and solar irradiation. The effects of catalyst dosage, initial pH and MO concentration on the removal efficiency were studied, and the photocatalytic reaction kinetics of MO degradation as well. The results indicated that Bi₄Nb_xTa_(1−x)O₈I exhibited high photocatalytic activity for the removal of MO in aqueous solutions. For example, the removal efficiency of MO by Bi₄Nb_0.1Ta_0.9O₈I was as high as 92% within 12 h visible light irradiation under the optimal conditions: initial MO concentration of 5-10 mg L⁻¹, catalyst dosage of 6 g L⁻¹ and natural pH (6-8), the MO molecules could be completely degradated by Bi₄Nb_0.1Ta_0.9O₈I within 40 min under UV light irradiation, and the photodegradation efficiency reaches to 60% after 7 h solar irradiation. Furthermore, the photocatalytic degradation of Bisphenol A (BPA) was also investigated under visible light irradiation. It is found that 99% BPA could be mineralized by Bi₄Nb_0.1Ta_0.9O₈I after 16 h visible light irradiation. Through HPLC/MS, BOD, TOC, UV-Vis measurements, we determined possible degradation products of MO and BPA. The results indicated that MO was degradated into products which are easier to be biodegradable and innocuous treated, and BPA could be mineralized completely. Furthermore, the possibility for the photosensitization effect in the degradation process of MO under visible light irradiation has been excluded.     

Mobility of radionuclides in soil/groundwater system: Comparing the influence of EDTA and four of its degradation products

The adsorption behavior of ²⁴¹Am, ⁶⁰Co, ¹³⁷Cs and ⁸⁵Sr in the presence and absence of chelating ligands (ethylenediaminetetraacetic acid, ethylenediaminediacetic acid, hydroxyethyliminodiacetic acid, iminodiaceiticacid and methyliminodiacetic acid) was investigated. Sorption affinity in the absence of chelating ligands followed: Am(III) > Co(II) > Cs(I) > Sr(II). The presence of chelating ligands generally had little effect on sorption of ⁸⁵Sr and ¹³⁷Cs with K_d values 110 and 690 mL g⁻¹, respectively. But at 0.02 M of ethylenediaminetetraacetic or hydroxyethyliminodiacetic, the K_d decreased to 5 or 63 mL g⁻¹, respectively, where thermochemical modeling indicated almost all ⁸⁵Sr is complexed with these ligands. The K_d values for ²⁴¹Am and ⁶⁰Co generally decreased with increasing chelating agent concentrations. In notable cases, the K_d values for Am increased at specific concentrations of 10⁻³ M for IDA, MIDA and 10⁻⁴ M for EDDA. This is proposed to be due to formation of a ternary surface complex.     

Heterogeneous reactions of suspended parathion, malathion, and fenthion particles with NO(3) radicals

Organophosphorus pesticides (OPPs) emit into the atmosphere in both gas and particulate phases via spray drift from treatments and post-application emission, but most of their degradations in the atmosphere are not well known. In this study, the heterogeneous reactions of nitrate (NO₃) radicals with three typical OPPs (parathion, malathion, and fenthion) absorbed on azelaic acid particles are investigated using an online vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The reaction products observed with the VUV-ATOFMS are identified on the basis of GC/MS analysis of the products in the reaction between NO₃ radicals and the coating of the pesticide. Paraoxon is identified as the only product of parathion; malaoxon and bis(1,2-bis-ethoxycarbonylethyl)disulfide as the products of malathion; fenoxon, fenoxon sulfoxide, fenthion sulfoxide, fenoxon sulfone, and fenthion sulfone as the products of fenthion. The degradation rates of parathion, malathion, and fenthion under the experimental conditions are 5.5 × 10⁻³, 5.6 × 10⁻², and 3.3 × 10⁻² s⁻¹, respectively. The pathways of the heterogeneous reactions between the three OPPs and NO₃ radicals are proposed. The experimental results reveal the possible transformations of these OPPs through the oxidation of NO₃ radicals in the atmosphere.     

Effects of growth substrate on triclosan biodegradation potential of oxygenase-expressing bacteria

Triclosan is an antimicrobial agent, an endocrine disrupting compound, and an emerging contaminant in the environment. This is the first study investigating triclosan biodegradation potential of four oxygenase-expressing bacteria: Rhodococcus jostii RHA1, Mycobacterium vaccae JOB5, Rhodococcus ruber ENV425, and Burkholderia xenovorans LB400. B. xenovorans LB400 and R. ruber ENV425 were unable to degrade triclosan. Propane-grown M. vaccae JOB5 can completely degrade triclosan (5 mg L⁻¹). R. jostii RHA1 grown on biphenyl, propane, and LB medium with dicyclopropylketone (DCPK), an alkane monooxygenase inducer, was able to degrade the added triclosan (5 mg L⁻¹) to different extents. Incomplete degradation of triclosan by RHA1 is probably due to triclosan product toxicity. The highest triclosan transformation capacity (T_c, defined as the amount of triclosan degraded/the number of cells inactivated; 5.63 × 10⁻³ ng triclosan/16S rRNA gene copies) was observed for biphenyl-grown RHA1 and the lowest T_c (0.20 × 10⁻³ ng-triclosan/16S rRNA gene copies) was observed for propane-grown RHA1. No triclosan degradation metabolites were detected during triclosan degradation by propane- and LB + DCPK-grown RHA1. When using biphenyl-grown RHA1 for degradation, four chlorinated metabolites (2,4-dichlorophenol, monohydroxy-triclosan, dihydroxy-triclosan, and 2-chlorohydroquinone (a new triclosan metabolite)) were detected. Based on the detected metabolites, a meta-cleavage pathway was proposed for triclosan degradation.     

Aqueous photoreduction of oxidized mercury species in presence of selected alkanethiols

Mercury is a global environmental contaminant with severe toxicity impact. The chemical processes resulting in the transformation of oxidized mercury species (Hg²⁺) to elemental mercury (Hg⁰), greatly affects the fate and transport of mercury in the natural environment. We hereby provide the first study on the photochemistry of Hg²⁺ with selected alkanethiols (R-SH) as model compounds to represent thiols and thiol-type binding sites on humic substances in natural waters because of the common sulfhydryl functional group (-SH). Kinetic studies were performed using cold vapor atomic fluorescence spectroscopy (CVAFS), the formation of Hg²⁺-thiol complexes (Hg(SR)₂) were confirmed by UV-visible spectrometry and Atmospheric Pressure Chemical Ionization-Mass Spectrometry (APCI-MS), and the reaction products were analyzed using Electron Impact-Mass Spectrometry (EI-MS) and Solid Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (SPME/GC-MS). Our results indicated that the photoreduction of Hg²⁺ by selected alkanethiols may be mediated by Hg²⁺-thiol complexes to produce Hg⁰. Under our experimental conditions, the apparent first order rate constants obtained for 1-propanethiol, 1-butanethiol, and 1-pentanethiol were (2.0 ± 0.2) × 10⁻⁷ s⁻¹, (1.4 ± 0.1) × 10⁻⁷ s⁻¹, (8.3 ± 0.5) × 10⁻⁸ s⁻¹, respectively. The effects of ionic strength, dissolved oxygen or chloride ion on reaction rates were found to be minimal under our experimental conditions. The identified products of the reaction between oxidized mercury species with selected alkanethiols (C₃-C₅) were Hg⁰ and disulfides (RS-SR). The potential environmental implications are herein discussed.     

Cross-sections and quantum yields for the atmospheric photolysis of the potent greenhouse gas nitrogen trifluoride

Although NF₃, a trace gas of purely anthropogenic origin with a large global warming potential is accumulating in the Earth's atmosphere, little photochemical data exists from which to calculate its atmospheric removal rate. In this study, photodissociation quantum yields, Φ₁, were derived following 193.3 nm laser photolysis of NF₃, and quantitative conversion of the F-atom photoproducts to OH, which was detected by laser induced fluorescence. Values of Φ₁(P, T) = (1.03 ± 0.05) were determined at pressures between 28 and 100 mBar of He or N₂ and at either room temperature or 255 K. Absorption cross-sections, σ, obtained between 184 and 226 nm were combined with the values of Φ₁(P, T) to confirm a long (≈700 year) photolysis lifetime for NF₃. No evidence for reaction of OH with NF₃ was found, indicating that this process makes little or no contribution to NF₃ removal from the atmosphere. These results underpin recent calculations of an NF₃ atmospheric lifetime τ ≈ 550 years, largely controlled by photolysis in the stratosphere. In the course of this work the rate coefficient k₂(298 K) = (1.3 ± 0.2) × 10^?11 cm³ molecule^?1 s^?1 was obtained for the reaction F + H₂O.